Optical record medium, optical record medium matrix, apparatus for manufacturing optical record medium, and optical recording/reproducing apparatus

ABSTRACT

The stable reproduction of wobble signal without generating beats despite of an improvement in recording density by narrowing a track pitch is realized. Data by magnetooptical recording is recorded on wobbling grooves ( 71 ) and lands ( 72 ) between adjacent wobbling grooves ( 71 ). The wobbling grooves ( 71 ) are provided to wobble both sides of the grooves in different amplitudes. Further, both the sides wobbled in different amplitudes are wobbled in phase in the track direction. These different amplitudes of both sides are preferably set to 3.3 to 40%.

TECHNICAL FIELD

[0001] The present invention relates to an optical recording medium, anoptical recording medium master, an apparatus for manufacturing opticalrecording medium master and an optical recording/reproducing apparatus.

BACKGROUND ART

[0002] An optical recording medium allows recording various signalizedinformation to optically reproduce. There are various kinds of recodingtype such as: read-only type optical discs in which embossed pitscorresponding to data are preformed on a disc substrate, such as compactdiscs and laser discs; magneto optical discs on/from which data isrecorded and reproduced utilizing a magnetooptical effect, such as MiniDiscs (MD); and phase-change optical discs on/from which information(data) is recorded and reproduced utilizing phase change of a recordinglayer, such as Digital Versatile Discs (DVD).

[0003] In the optical recording medium capable of rewriting information,such as magneto optical discs and phase-change optical discs, contiguousgrooves instead of discrete pits are formed along a recording track. Thegrooves are provided for mainly controlling tracking servo, so-calledguide grooves. The interspaces between the grooves are called landsbecause they protrude in the position close to the surface of thegrooves than the bottom thereof.

[0004] The optical recording medium formed with the grooves generallyperforms a tracking servo control by using a push-pull signal. In orderto obtain the push-pull signal, a light beam is irradiated toward theoptical recording medium and the light reflected by the opticalrecording medium is detected with two photodetectors placed symmetricalto the center of the track, thereby the push-pull signal can be obtainedbased on a difference in the outputs from two photodetectors.

[0005] The applicant has proposed a method of forming wobbling widegrooves, which is a data recording area of MD, by superimposing thesignals of 22.05 kHz and 5 MHz in Japanese Patent No. 2960018. In thismethod, FM modulation signal of 22.05 kHz is for recording wobbleinformation of address, whereas the signal of 5 MHz is for widening thegroove width in accordance with the amplitude. With this method, thewobbling wide grooves are formed to wobble both sides of the grooves.The data recording area becomes wide grooves by forming the wobblingwide grooves in the optical recording medium. This achieves the stablereproduction of wobble signal of ADIP and the stablerecording/reproducing of MO signal.

[0006] Japanese Patent No. 2854187 proposes the technique that one sideof the grooves is wobbled and the other side is not wobbled but instraight (circular arc). According to the technique, address informationcan be stored in the wobbles of the grooves.

[0007] A high recording density and the stable reproduction of thewobble signal are required in the optical recording medium formed withthe wobbling grooves.

[0008] However, in the optical recording medium in which one side of thegrooves are wobbled as disclosed in Japanese Patent No. 2854187, theother side of the grooves which is not wobbled is not used for storingthe address information. As a result, the wobble signal amount is abouthalf of the optical recording medium in which both sides of the groovesare wobbled, thereby resulting in a problem of the difficulty of thestable reproduction of the wobble signal.

[0009] In addition, the stable reproduction of the wobble signal isdesired by increasing the wobble signal amount. However, in order toform the grooves in which both sides thereof are wobbled and to improvethe recording density, it is necessary to narrow a track pitch. Thenarrow track pitch generates beats in the wobble signal between theneighboring wobbles specifically in case of an out-of-phase wobble. Thisresults in the problem of the difficulty of the stable reproduction ofthe wobble signal.

[0010] The present invention has been achieved in view of the aboveproblems. It is an object of the invention to provide an opticalrecording medium capable of stably reproducing the wobble signal withoutgenerating beats even if the track pitch is narrowed to improve therecording density. Further, the present invention provides an opticalrecording/reproducing apparatus used for recording/reproducing on/fromthe optical recording medium, an optical recording medium master usedfor replicating the optical recording medium and an apparatus formanufacturing optical recording medium master.

DISCLOSURE OF THE INVENTION

[0011] The optical recording medium and the optical recording mediummaster of the invention have grooves on a surface of a substrate toconstitute a groove track and are able to read information along a trackof the grooves. The grooves are wobbling grooves provided to wobble bothsides of the grooves in different amplitudes.

[0012] Another optical recording medium and the optical recording mediummaster of the invention have grooves on a surface of a substrate toconstitute a groove track and are able to read information along a trackof the grooves. The grooves are wobbling grooves provided to wobble bothsides of the grooves in phase in different amplitudes.

[0013] A manufacturing apparatus for the optical recording medium masterof the invention patterns grooves forming a track on a surface of amaster, wherein a light beam for exposure or a laser beam is relativelytraveled on a surface of a master of an optical recording medium withwaving at a certain period in a direction intersect with a travelingbased on a control signal superimposing a low-frequency signal and ahigh-frequency signal, and a latent image is formed to become wobblinggrooves wobbles both sides of the grooves in phase in differentamplitudes.

[0014] An optical recording/reproducing apparatus of the inventionrecords and/or reproduces information on/from an optical recordingmedium having wobbling grooves provided to wobble both sides of groovesin different amplitudes and recording information both on the wobblinggrooves and on lands, comprises: a means for traveling a light spot onthe wobbling grooves; and a means for detecting a wobble signal bytraveling the light spot on the wobbling grooves.

[0015] Another optical recording/reproducing apparatus of the inventionrecords and/or reproduces information on/from an optical recordingmedium having wobbling grooves provided to wobble both sides of groovesin different amplitudes and recording information either on the wobblinggrooves or on lands, comprises: a means for traveling a light spot onthe wobbling grooves; and a means for detecting a wobble signal bytraveling the light spot on the wobbling grooves.

[0016] In the optical recording medium, the master for the opticalrecording medium, the manufacturing apparatus of the master for theoptical recording medium and the optical recording/reproducing apparatusof the invention, the grooves are wobbling grooves provided to wobbleboth sides of the grooves thereof in different amplitudes. Further, bothsides wobble in different amplitudes are wobbled in phase in the trackdirection. These different amplitudes of both sides are preferably setto 3.3 to 40%.

[0017] Other and further objects, features and advantages of theinvention will appear more fully from the following description.

BRIEF DESCRIPTION OF THE DRAWINGS

[0018]FIG. 1 shows a schematic structure of a magneto optical discaccording to an embodiment of the invention.

[0019]FIG. 2 is an enlarged view showing a recoding area formed on asurface of the magneto optical disc shown in FIG. 1.

[0020]FIG. 3 shows a schematic structure of a laser cutting apparatusfor producing a master for the magneto optical disc of an embodiment ofthe invention.

[0021]FIG. 4 schematically shows an exposure method for forming thewobbles having different amplitudes on both sides of wobbling grooves inphase.

[0022]FIG. 5 shows a schematic structure of the wobbling groovesobtained by the exposure method shown in FIG. 4.

[0023]FIG. 6 shows the results of the measurement of jitter as a typicalvalue of recoding/reproducing characteristic of the evaluation magnetooptical disc.

BEST MODE FOR CARRYING OUT THE INVENTION

[0024] A preferred embodiment of the present invention will be describedin more detail below referring to the accompanying drawings.

[0025] [Magneto Optical Disc]

[0026]FIG. 1 shows a schematic structure of a magneto optical disc of anembodiment of the invention. The magneto optical disc is a disc shapedoptical recording medium recoding/reproducing data by the magnetoopticaleffect compliant with MD3 format standards.

[0027] A recoding area 3 recoding magnetooptically, a protective layer 4covering the whole surface of the recording area for protection arelaminated in this order on a disc substrate 2 made of glass,polymethylmethacrylate (PMMA) or polycarbonate (PC). Although not shownin FIG. 1, the recoding area 3 comprises, for example, a firstdielectric film made of SiN (silicon nitride), a perpendicular recordingfilm made of a TeFeCo alloy, a second dielectric film made of SiN, areflective film made of an Al alloy or the like in this order. Theprotective layer 4 is formed on the recording area 3 by spin coating anultraviolet curing resin. The materials for the recording area 3 and theprotective layer 4 are not limited to the above. The materials capableof effective magnetooptical recording can be used for forming therecording area 3. Any kinds of materials which can effectively protectthe recording area 3 can be used for forming the protective layer 4.

[0028]FIG. 2 is an enlarged view of the recording area formed on asurface of the magneto optical disc. The recording area can writemagnetooptical recoding data on wobbling grooves 71 and lands 72 formedbetween the adjacent wobbling grooves 71.

[0029] The wobbling grooves 71 have an amplitude of ±15 nm on one side(the right side in FIG. 2) and an amplitude any of ±0.5 nm, ±1.5 nm,±3.0 nm or ±6.0 nm on the other side, for instance, and wobble atsubstantially constant period in phase in the longitudinal direction ofthe wobbling grooves 71. The track pitch is 1.2 μm and the widths of thesubstantial writing area of the wobbling grooves 71 and the lands 72 areabout 0.60 μm. The track pitch is the distance between the centers ofthe wobbles of the neighboring tracks.

[0030] The magneto optical disc is a Land and Groove Format in which theaverage widths of the wobbling grooves 71 and the lands 72 areapproximately equal. Therefore, enough level of push-pull signal can beobtained to perform the tracking servo control. The push-pull signal canbe obtained based on a difference between output SA and output SB(SA−SB). The outputs SA and SB can be determined by detecting thereflected light obtained by irradiating a light beam toward the magnetooptical disc with two photodetectors A and B (not shown) placedsymmetrical to the center of the track. The amount of reflective lightcan be determined by the sum of the output SA from the photodetector Aand the output SB from the photodetector B (SA+SB). The detectedinformation of the amount of reflective light (the sum signal of SA+SB)is used for detecting the number of straddle of the tracks when a lightbeam spot travels across the wobbling grooves 71 in the width directionthereof. This is generally called a cross track signal.

[0031] As described, the wobbling grooves 71 are provided to wobble bothsides in phase in different amplitudes and the address information isstored (added or included) in the wobbling grooves 71. As a result,compared to the case where the wobbling grooves 71 are provided towobble one side thereof, the wobble signal amount is increased by 3.3%to 40%. Moreover, the wobbles on both sides are in phase and theamplitude of one side of the wobbling grooves 71 is ±15 nm and the otherside is ±6.0 nm at the maximum, so when both sides of the wobblinggrooves 71 are wobbled, sufficient signal amount can be obtained. Inaddition, the beats generated in the wobble signal during therecording/reproducing information can be reduced or eliminated, therebythe stable recording/reproducing is achieved.

[0032] Furthermore, enough push-pull signal for the tracking servocontrol can be obtained from both wobbles of the wobbling grooves 71having different amplitudes. This enables to perform the sure trackingstably.

[0033] [Laser Cutting Apparatus and Fabrication of Master using theSame]

[0034] A master (a master for manufacturing the optical recordingmedium) is used for manufacturing the magneto optical disc by, forexample, an injection molding apparatus. The master is manufactured bythe laser cutting apparatus shown in FIG. 3.

[0035] The laser cutting apparatus exposes a photoresist 12 applied on aglass substrate 11 and forms a latent image of the planar pattern suchas the wobbling grooves 71.

[0036] In the manufacturing process of the master, first, the glasssubstrate 11 applied with the photoresist 12 thereon is set on aturntable 17 of a rotative driving device (not shown). In the exposureprocess of the photoresist 12, the glass substrate 11 with thephotoresist 12 is rotative driven by the turntable 17 as indicated by anarrow M in the figure. Moving optical table 18 irradiates a laser beam30 on the photoresist 12 while moving in parallel. Thereby, a desiredpattern is exposed on the whole photoresist 12 on the glass substrate11.

[0037] Specifically, the relative rotational speed (linear speed) of themaster by the turntable 17 to the laser beam 30 during the exposure is0.91 m/s and the moving optical table 18 moves in parallel by the trackpitch of 1.20 μm per rotation, for instance. The rotational speed andthe absolute value of the track pitch are not limited to this.

[0038] More specifically, as a laser light source system, a laser lightsource 13 emitting laser light, an EOM (Electro Optical Modulator) 14for adjusting the intensity of the laser light emitted from the laserlight source 13, a BS (Beam Splitter) 16 for dividing the laser lightemitted form the EOM 14 into transmitted light and reflective light, ananalyzer 15 placed on the light axis of the laser light emitted from theEOM 14, a PD (Photo Detector) 19 receiving the laser light pass throughthe analyzer 15 and APC (Auto Power Controller) 20 for feedbackcontrolling of the intensity of the laser light emitted from the EOM 14with applying the signal electric field to the EOM 14 are comprised.

[0039] Kr (krypton) laser having a wavelength λ of 351 nm or the like,which can emit short wavelength laser light, is desirable as the laserlight source 13, although this is not limited.

[0040] The laser light emitted form the laser light source 13 areadjusted to a predetermined light intensity by EOM 14 which iscontrolled and driven by the APC 20 and enters the analyzer 15. Here,the analyzer 15 is S polarized light, so the laser light pass throughthe analyzer 15 becomes S polarized light.

[0041] The laser light which is emitted from the laser light source 13and travels straight via the EOM 14, the BS 16 and the analyzer 15 isreceived by the PD 19. The PD 19 detects the light intensity and sendsthe signal storing information of the light intensity to the APC 20.Upon receiving the signal, the APC 20 adjust the signal electric fieldby entering the control signal to the EOM 14 to uniform the laser lightintensity received by the PD 19. The automatic control of the lightamount of the laser light source system keeps the constant intensity ofthe laser light emitted from the EOM 14.

[0042] On the other hand, the laser light reflected by the BS 16 travelsas a parallel beam is reflected by a mirror 21 to change the directionand conducted to an AOD (Acoustic Optical Deflector) 48 in the movingoptical table 18.

[0043] The moving optical table 18 comprises the AOD 48, a drive circuit50, a reflective mirror 22, a beam magnifying lens 55 and an objectivelens 54. The AOD 48 comprises an acoustic optical element 46 and wedgeprisms 47 and 49 placed front and the back of the light axis of theacoustic optical device 46. These are placed to make the lattice planeof the acoustic optical element 46 and the wedge prisms 47 and 49satisfy the Bragg's condition of diffraction and not to change thehorizontal height of the light axis. As the acoustic optical element 46,tellurium oxide (TeO₂) can be preferably used. The AOD 48 is controlledbased on the DC signal from the drive circuit 50 to modulate the laserlight intensity.

[0044] A voltage frequency controller 51 provides a high-frequencysignal to the drive circuit 50. The control signal is externallyprovided to the voltage frequency controller 51. The control signal hasa waveform in which a sinusoidal wave signal having a frequency of 5 MHzis superimposed on a sinusoidal wave signal having a frequency of 84.672kHz. The sinusoidal wave of a frequency of 84.672 kHz wobbles the planerpattern of the wobbling grooves 71, while the amplitude of thesinusoidal wave of a frequency of 5 MHz widen the groove width of theplaner pattern of the wobbling grooves 71.

[0045] The control signal controls the AOD 48 to change the Braggdiffraction angle of the acoustic optical element 46 in the AOD 48. Thisgenerates the wobbles storing the address information in the laser beam30. At this time, the laser beam 30 is controlled to have a constantspot and converged on the master.

[0046] More specifically, in order to widen the width of the wobblinggrooves 71, a spatial frequency of polarization frequency is adjustedand made multiple exposures to become smaller amplitude than a radius oflaser beam 30 irradiating on the master. In other words, assuming thelinear speed of the laser beam 30 relatively traveling on the master isv, the polarization frequency is f, a diameter of the laser beam is D,v/f≦D. For example, when v=0.91 m/s, D=0.35 μm and f is 2.6 MHz or more(f≧2.6 MHz), the width of the wobbling grooves 71 can be widened.

[0047]FIG. 4 schematically shows an exposure method for forming thewobbles having different amplitudes on both sides of the wobblinggrooves 71 in phase, as described above. FIG. 5 schematically shows thewobbling grooves 71.

[0048] A D/A converter provided with an external reference voltage andcapable of obtaining the output in proportion to the external voltage isprepared. The clockpulse double the frequency of 5 MHz is applied andthe level data equivalent to 100% output and 50% output, respectively isrepeatedly applied. The external reference voltage is voltage in whichoffset equivalent to 50% of reference voltage Vs is applied to thelow-frequency wobble signal. For example, the external reference voltageVo is Vo=Vs×0.5 (direct current)+low-frequency wobble signal (10% pp).If necessary, DC offset is applied to the output signal to eliminate thedirect current component.

[0049] The envelope of the positive side of the high-frequency signalwaveform (this defines the right side in FIG. 4) is 10% pp, whereas theenvelope of the negative side (this defines the left side in FIG. 4) is5% pp. This enable to obtain the control signal whose ratio of theamplitude of the envelope waveform of the positive side and the negativeside of the high-frequency signal waveform is 2:1. However, the ratio ofthe amplitude of the envelope waveform is not limited to the above.

[0050] Variation of the ratio of the level data applied to the D/Aconverter can vary the modulation degree of the envelope waveform.Making one of the level data a negative voltage reverses the phase ofthe negative side and the positive side, thereby enabling the wobbles onboth sides of the wobbling grooves 71 become mutually the oppositephase. It is possible to vary the amplitude of the high-frequency signalby changing the direct current offset voltage applied as the externalreference voltage.

[0051] The control signal generated as described above is applied to thedrive circuit 50 as a signal corresponding to the exposure pattern fromthe voltage frequency controller 51 during the exposure of thephotoresist 12. Based on the signal, the drive circuit 50 drives the AOD48, optical polarization is performed on the laser beam 30 for exposingthe photoresist 12, and the planar pattern of the wobbling grooves 71wobbling both sides thereof in phase in different amplitudes can beexposed on the photoresist 12 of the master.

[0052] Specifically, when storing the address information by wobblingthe wobbling grooves 71 with a frequency of 84.672 kHz, thelow-frequency signal and the high-frequency signal, which are FMmodulated into 84.672 kHz and 5 MHz, respectively by use of ahigh-frequency signal having a center frequency of 224 MHz, aresuperimposed to generate the control signal. The obtained control signalis applied to the drive circuit 50 from the voltage frequency controller51. Based on the applied signal, the drive circuit 50 changes the Braggangle of the acoustic optical device 46 of the AOD 48, the polarizationis performed acoustic optically on the laser beam 30, and the patternwobbled both sides in phase in different amplitudes can be exposed.

[0053] The laser beam 30 applied the acoustic optical polarization bythe AOD 48 is adjusted to a predetermined beam spot diameter by the beammagnifying lens 55, reflected by the mirror 22 and conducted to theobjective lens 54. After that, the laser beam 30 is irradiated on thephotoresist 12 on the master by the objective lens 54 while waving inthe direction intersect with the groove direction of the wobblinggrooves 71 as shown in FIG. 4. Thereby, the latent image including thepattern which wobbles both sides of a wobbling grooves 71 in phase indifferent amplitudes is formed on the photoresist 12. The planer patternof the wobbling grooves 71 wobbles both sides thereof in differentamplitudes is exposed by periodically waving one beam spot withdifferent amplitudes based on the control signal superimposing thelow-frequency signal and the high-frequency signal. As a result, nophase lag (or synchronous lag) is generated on both sides of the wobblesunlike the case where the wobbles on both sides of a wobbling groove 71is exposed by using the different beam spots. This ensures the exposureof the wobbles on both sides in phase.

[0054] It is preferable for the objective lens 54 to have a larger NA(numerical aperture) in order to form the smaller loop pattern with ahigh accuracy. Specifically, the objective lens 54 with an NA of 0.9 ormore is preferable.

[0055] After forming the latent image on the photoresist 12 on themaster, the master is developed by dissolving exposed part of thephotoresist 12. In particular, an undeveloped master is set on theturntable of processor, which is not shown. Then it is rotated with theturntable and developer is dropped on the surface of the master todevelop the photoresist 12.

[0056] Subsequently, a conductive film of nickel (Ni) thin film isformed on the uneven pattern of the photoresist 12 on the master byelectroless plating machine (not shown). The master formed with theconductive film is set on the gilding machine, which is not shown, and anickel-plating layer with a thickness of about 300±5 μm is formed on theconductive film by electroplating, for example.

[0057] Then, the nickel-plating layer is separated from the master bycutter, squeegee for separation or the like and the photoresist 12remaining on the surface in which the nickel-plating layer was formed iscleaned using acetone or the like to obtain stamper incorporated in amold for an injection molding.

[0058] Using the stamper, the minute concavity and convexity in thewobbling grooves 71 and so on formed on the surface of the master aretransferred on a surface of a base plate 1 by photopolymerizationprocess (the so-called 2P process). For example, first, photopolymer isevenly applied on the surface formed with the concavity and convexity ofthe master to form a photopolymer layer 7. On the photopolymer layer 7,the base plate 1 of glass with a thickness of 1.2 mm and a refractiveindex of 1.52 or less is adhered while avoiding the mix of air bubble,dust and the like. Then, the photopolymer layer 7 is hardened byultraviolet irradiation, and is separated form the master together withthe base plate 1. Thereby, the disc substrate 2 on which the minuteconcavity and convexity of the surface of the master is transferred onthe photopolymer layer 7 can be obtained.

[0059] A first dielectric film made of silicon nitride (Si₃N₄), a DWDD(Domain Wall Displacement Detection) film made of a TbFeCo alloy, aDyFeCo alloy, a GdFe alloy or the like, a second dielectric film made ofsilicon nitride and a reflective film made of an aluminum alloy (Al—Ti)are deposited in this order on the recording surface of the discsubstrate 2 as shown in FIG. 1 as the recording area 3. After that, onthe reflective film, 2P resin is smoothly applied to cover almost wholesurface (top surface) of the substrate by, for example, spin coat methodand hardened by irradiating UV lamp to form the protective layer 4.Thereby, the magneto optical disc of the embodiment is achieved.

[0060] In the embodiment, as a method that the concavity and convexitypattern of the wobbling grooves 71 or the like formed on the master isprecisely transferred on the disc substrate 2, a method usingphotopolymer is described. However, in case of mass production with highefficiency of the disc substrate 2, a transparent resin such aspolymethylmethacrylate and polycarbonate may be formed with injectionmolding to manufacture the disc substrate 2 formed with the concavityand convexity pattern of the wobbling grooves 71 thereon.

[0061] The materials for forming the base plate 1, the recording area 3,the protective layer 4 or the like of the magneto optical disc is notlimited to the materials described above, so other materials can beused.

EXAMPLE

[0062] A plural evaluation magneto optical discs having the variousamplitude of the wobbling grooves or the like were fabricated by themethod using the master as described and the recording/reproducingcapability were evaluated on each evaluation magneto optical disc.

[0063] In order to conduct an evaluation experiment of the evaluationmagneto optical discs, first, the masters were fabricated. In themanufacturing process of the masters, the power of the laser beam 30 forexposure was varied to check the change in the groove width per power.Specifically, the power of the laser beam 30 was set to 0.9, 1.1 and1.45 and the widths of the wobbling grooves 71 of the masters weremeasured on each case by use of an electron microscope. The groovewidths were 562 nm, 622 nm and 682 nm in accordance with the abovepowers, respectively. Each amplitudes of one side of the disc was ±15nm, and the other sides were set to have different amplitudes of ±0.5nm, ±1.5 nm, ±3.0 nm and ±6.0 nm, respectively.

[0064] Using the masters fabricated as described above, the discsubstrate 2 was formed by the above-described photopolymer process andthe recording area 3 and the protective layer 4 were formed on thesurface thereon to fabricate the evaluation magneto optical discs.

[0065] The reproducing characteristics of the wobble signal and therecording/reproducing characteristics of the magnetooptical recordinglayer were measured on each evaluation magneto optical discs fabricatedas described above. The optical pickup in which a wavelength λ of laserlight is 650 nm and NA of the objective lens 54 is 0.52 was used for themeasurement and the reading and reproducing were performed on thewobbling grooves 71 and the lands 72 with 1-7 modulation.

[0066] The results showed the stable reproduction of the wobble addresssignal in all evaluation magneto optical discs.

[0067] Further, the jitter as a typical value (parameter) of therecording/reproducing characteristics in the magnetooptical recordinglayer was measured on the evaluation magneto optical disc in which theamplitude of one side of the wobbling grooves 71 was ±15 nm and theother side thereof was ±6.0 nm. The results are shown in FIG. 6. Namely,when the groove width was 562 nm, the jitter in the lands 72 was 10.5%and the jitter in the wobbling grooves 71 was 9.5%. Further, when thegroove width was 622 nm, the jitter in the lands 72 was 9.5% and thejitter in the wobbling grooves 71 was 8.5%. Furthermore, when the groovewidth was 682 nm, the jitter in the lands 72 was 10.0% and the jitter inthe wobbling grooves 71 was 8.5%. The recording/reproducingcharacteristics of all evaluation magneto optical discs were stableenough. In the case where the amplitude of the other side of thewobbling grooves 71 is less than ±6.0 nm, it is assumed that furtherstable recording/reproducing characteristics can be obtainedtheoretically. In fact, it was confirmed that the recording/reproducingcharacteristics measuring the jitter as a typical value was more stable.

[0068] In all evaluation magneto optical discs in which the amplitude ofone side of the wobbling grooves 71 was ±15 nm and the other sidethereof were within the range between 0.5 nm at the minimum and 6.0 nmat the maximum, the stable recording/reproducing characteristics wasobtained. It revealed that setting the ratio of amplitude of one side ofthe wobbling grooves 71 having a smaller amplitude to the other sidethereof having a larger amplitude within the range from 3.3% to 40%enabled to obtain the stable recording/reproducing characteristics.

[0069] The invention is wildly applicable to an optical recording mediumcapable of forming different amplitudes of the wobble in both sides ofthe grooves, a master and a manufacturing method thereof and an opticalrecording apparatus.

[0070] The invention is also applicable to a rewritable opticalrecording medium capable of rewriting data more than once, a recordableoptical recording medium capable of recording and incapable of deletingand a read-only optical recording medium in which data incapable ofrewriting is prerecorded.

[0071] In addition, the invention is applicable to any recording type ofdata such as a read-only type, a magnetooptical typerecording/reproducing data utilizing the magnetooptical effect and aphase-change type recoding/reproducing data using the phase change ofthe recording layer.

[0072] Furthermore, the invention is applicable to the optical recordingmedium in which the data recording area is formed only in the lands,only in the grooves, or both the lands and the grooves as well as theoptical recording medium in which the embossed pits and the wobblinggrooves are formed together in one disc.

[0073] As described, the optical recording medium, the optical recordingmedium master, manufacturing apparatus of the optical recording mediummaster and the optical recording/reproducing apparatus of the invention,the grooves are the wobbling grooves provided to wobble both sides ofthe grooves in different amplitudes. Further, both sides of the groovesare wobbled in phase in the track direction. As a result, even if thetrack pitch is narrowed to improve the recording density, the effectsuch that the stable wobble signal is reproduced without generatingbeats are achieved.

[0074] Obviously many modifications and variations of the presentinvention are possible in the light of the above teachings. It istherefore to be understood that within the scope of the appended claims,the invention may be practiced otherwise than as specifically described.

1. An optical recording medium in which grooves are formed on a surfaceof a substrate to constitute a groove track and information can be readalong a track of the grooves, wherein the grooves are wobbling groovesprovided to wobble both sides of the grooves in different amplitudes. 2.An optical recording medium according to claim 1, wherein the wobblinggrooves have a ratio of amplitude of one side of the wobbling grooveshaving a smaller amplitude to the other side thereof having a largeramplitude within the range from 3.3% to 40%.
 3. An optical recordingmedium according to claim 1, wherein information can be recorded ongrooves of the wobbling grooves and on lands between the adjacentwobbling grooves.
 4. An optical recording medium in which grooves areformed on a surface of a substrate to constitute a groove track andinformation can be read along a track of the grooves, wherein thegrooves are wobbling grooves provided to wobble both sides of thegrooves in phase in different amplitudes.
 5. An optical recording mediumaccording to claim 4, wherein the wobbling grooves have a ratio ofamplitude of one side of the wobbling grooves having a smaller amplitudeto the other side thereof having a larger amplitude within the rangefrom 3.3% to 40%.
 6. An optical recording medium according to claim 4,wherein information can be recorded on grooves of the wobbling groovesand on lands between the adjacent wobbling grooves.
 7. An opticalrecording medium master used for manufacturing an optical recordingmedium in which grooves are formed on a surface of a substrate toconstitute a groove track and information can be read along a track ofthe grooves, wherein the grooves are wobbling grooves provided to wobbleboth sides of the grooves in different amplitudes.
 8. An opticalrecording medium master according to claim 7, wherein the wobblinggrooves have a ratio of amplitude of one side of the wobbling grooveshaving a smaller amplitude to the other side thereof having a largeramplitude within the range from 3.3% to 40%.
 9. An optical recordingmedium master according to claim 7, wherein an optical recording mediumin which information can be recorded on grooves of the wobbling groovesand on lands between the adjacent wobbling grooves is manufactured. 10.An optical recording medium master in which grooves are formed on asurface of a substrate to constitute a groove track and information canbe read along a track of the grooves, wherein the grooves are wobblinggrooves provided to wobble both sides of the grooves in phase indifferent amplitudes.
 11. An optical recording medium master accordingto claim 10, wherein the wobbling grooves have a ratio of amplitude ofone side of the wobbling grooves having a smaller amplitude to the otherside thereof having a larger amplitude within the range from 3.3% to40%.
 12. An optical recording medium master according to claim 10,wherein an optical recording medium in which information can be recordedon grooves of the wobbling grooves and on lands between the adjacentwobbling grooves is manufactured.
 13. A manufacturing apparatus for anoptical recording medium master patterning grooves forming a track on asurface of a master, wherein a light beam for exposure or a laser beamis relatively traveled on a surface of a master of an optical recordingmedium with waving at a certain period in a direction intersect with atraveling based on a control signal superimposing a low-frequency signaland a high-frequency signal, and a latent image is formed to becomewobbling grooves wobbles both sides of the grooves in phase in differentamplitudes.
 14. A manufacturing apparatus for an optical recordingmedium master according to claim 13, wherein wobbles on both the sidesare kept in phase and amplitudes of the wobbles on both the sides areindependently controlled.
 15. A manufacturing apparatus for an opticalrecording medium master according to claim 13, wherein the wobblinggrooves have a ratio of amplitude of one side of the wobbling grooveshaving a smaller amplitude to the other side thereof having a largeramplitude within the range from 3.3% to 40%.
 16. An opticalrecording/reproducing apparatus recording/reproducing informationon/from an optical recording medium having wobbling grooves provided towobble both sides of grooves in different amplitudes and recordinginformation both on the wobbling grooves and on lands, comprising: ameans for traveling a light spot on the wobbling grooves; and a meansfor detecting a wobble signal by traveling the light spot on thewobbling grooves.
 17. An optical recording/reproducing apparatusrecording/reproducing information on/from an optical recording mediumhaving wobbling grooves provided to wobble both sides of grooves indifferent amplitudes and recording information either on the wobblinggrooves or on lands, comprising: a means for traveling a light spot onthe wobbling grooves; and a means for detecting a wobble signal bytraveling the light spot on the wobbling grooves.